1. Field of the Invention
This invention relates to an image forming apparatus such as an electrophotographic type analog-digital copying machine, a color copying machine, a printer or a page printer.
2. Related Background Art
When image formation is to be done at a high speed, for example, in an electrophotographic type image forming apparatus, the image forming speed thereof has been realized by effecting, in addition to the supply and conveyance of transfer paper which is a sheet, an image forming process, i.e., a series of operations such as latent image formation, development, the transfer of a toner image to a transfer sheet and fixing at a high speed. For example, to realize an image forming apparatus capable of forming 60 sheets of images per minute in contrast with an image forming apparatus capable of forming 30 sheets of images per minute, the driving speed necessary for the image forming process, in addition to the supply and conveyance of the transfer sheet, has been set to two times.
In the above-described example of the prior art, however, in order to realize high-speed image formation, it has been required to effect the image forming process at a high speed, in addition to the conveyance of the transfer sheet, and large-scaled studies have been required.
Thus, for example, in the latent image formation in the image forming process, it is necessary in a digital image forming apparatus to operate image processing and latent image forming means such as a laser at a high speed, and when for example, development from an image forming apparatus capable of forming 30 sheets of images per minute to an image forming apparatus capable of forming 60 sheets of images per minute is to be done, the image processing portion or the like in which the image clock frequency thereof has been made double has been required.
Also, in an analog image forming apparatus, it has been necessary to double the driving speed of an original scanner for scanning an original to be copied.
Further, in both apparatuses, the image forming process such as the development and transfer of a toner image is, as it were, the most important technique in an electrophotographic type image forming apparatus, and a long study time has been required until the constructing and technique thereof are determined, and a great deal of resources have been required for the development of an image forming apparatus accompanying high-speed image formation.
The present invention has as its object to provide an image forming apparatus of high image forming efficiency and high productivity which narrows the interval between sheets fed to an image forming portion, without changing the image forming process speed.
The image forming apparatus of the present invention is provided with sheet supporting means on which sheets are supported, sheet feeding means for feeding said sheets from said sheet supporting means, sheet conveying means for conveying said sheets fed by said sheet feeding means to the vicinity of image forming means for forming images on said sheets, image forming and conveying means for conveying said sheets conveyed by said sheet conveying means into said image forming means for image formation, and control means for controlling the sheet conveying speeds of said sheet feeding means, said sheet conveying means and said image forming and conveying means, said control means being adapted to control so that the sheet conveying speed may become higher in the order of said sheet feeding means, said image forming and conveying means and said sheet conveying means.
In the above-described image forming apparatus of the present invention, the control means controls so that the sheet conveying speed may become higher in the order of the sheet feeding means, the image forming and conveying means and the sheet conveying means and therefore, the sheets are slowly and reliably supplied from the sheet supporting means, and are rapidly conveyed to the vicinity of the image forming means to thereby shorten the conveying time, whereafter the sheets are slowly conveyed and images are reliably formed on the sheets by the image forming means.
Therefore, the image forming apparatus can be made high in speed without changing the image forming process speed.
The image forming apparatus of the present invention is such that said control means controls said sheet feeding means so that the sheet conveying speed may continuously or stepwisely increase from the sheet stopped state to a predetermined sheet conveying speed.
The image forming apparatus of the present invention is such that said sheet feeding means, said sheet conveying means and said image forming and conveying means are provided with individual drive sources.
The image forming apparatus of the present invention is such that since the drive sources of said sheet feeding means, said sheet conveying means and said image forming and conveying means are individual, the control of each means by the control means becomes easy.
The image forming apparatus of the present invention is such that said sheet conveying speed is a speed at which the sheet is conveyed when said drive sources have assumed their constant operative states from their started states.